Protein delivery to cells, for example protein delivery for therapeutic purposes, or gene therapy, is typically achieved by one of two approaches to deliver of the therapeutic sequence. One approach uses naked nucleic acid or non-viral vectors Another approach uses viral vectors. Viral vectors can be non-integrative, like adenovirus (Ad) or herpesvirus (HSV), or integrative, like adeno-associated virus (AAV) and retroviruses (e.g. MLV). In the case of Ad and HSV the expression of the therapeutic gene is only transient. In the case of integrative vectors, retroviruses or AAV, there is a long-term (and theoretically cell-life time) expression.
These gene therapy approaches have several drawbacks, including transfer efficiency or oncogenic integration events. Viral vectors inevitably induce neutralizing antibodies or meet pre-existing antibodies in their hosts and this limits the efficiency of gene transfer and the life-time of transduced cells. All viral vectors, even replication-defective ones, have the theoretical possibility to revert back to a replicative form, and/or to recombine with another virus of the same or related family present at the same time in the same host. In addition, the viral genome may insert itself into an essential region causing other problems. Thus, transfer of such material is associated with biological risks and thus requires careful consideration of bio safety.
To address these issues safer and more efficient synthetic vectors for nucleic acid transfer are needed.
Virus Like Particles (VLPs) are structures resembling a virus particle but devoid of the viral genome. Accordingly they are incapable of replication and devoid of pathogenicity. A VLP typically comprises at least one type of structural protein from a virus.
In most cases this protein will form a proteinaceous capsid (e.g. VLPs comprising a retrovirus, adenovirus or bacteriophage structural protein). In some cases the capsid will also be enveloped in a lipid bilayer originating from the cell from which the assembled VLP has been released.
VLPs are typically formed when a gene encoding a viral structural protein is overexpressed in a host cell in isolation from other viral genes. In the cytosol, the structural proteins assemble into the VLP in a process analogous to the process in which a bona fide virus particle assembles. Formation of VLPs results in their release from the host cell. In most cases, VLPs are used for making antibodies using only GAG or structural proteins. It might also possible to assemble VLPs in vitro. Enveloped virus-like particles can be engineered to be fusogenic and thus capable of delivering both membrane bound and non-membrane-bound proteins to cells.
The present invention makes use of virus-like particles (VLPs) as delivery vehicles for proteins to cells.
There is a need in the art for safer, more effective delivery and targeting of protein to cells, which is satisfied by the present invention.